Method and apparatus for performing neuroimaging

ABSTRACT

The present invention relates to systems and methods of performing magnetic resonance imaging (MRI) in awake animals. The invention utilizes head and body restrainers to position an awake animal relative to a radio frequency dual coil system operating in a high field magnetic resonance imaging system to provide images of high resolution without motion artifact.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No.: 09/694,087, filed Oct. 20, 2000, now U.S. Pat. No. 6,711,430which is a continuation-in-part of U.S. patent application Ser. No.09/073,546, filed on May 6, 1998, now abandoned both of which are herebyincorporated by reference in their entirety.

GOVERNMENT SUPPORT

The invention was supported, in whole or in part, by a grant R42MH59501from National Institutes for Health. The Government has certain rightsin the invention.

BACKGROUND OF THE INVENTION

The present invention relates to magnetic resonance imaging, and moreparticularly to a method and apparatus for performing functional magnetiresonance imaging (fMRI) in conscious animals.

Human studies utilizing fMRI have advanced our understanding of theregional and functional interplay between populations of neurons servingsensory, integrative and motor functions. Changes in neuronal activityare accompanied by specific changes in hemodynamics such as cerebralblood flow, cerebral blood volume, and blood oxygenation. Functional MRIhas been used to detect these changes in response to visual stimulation,somatosensory activation, motor tasks, and emotional and cognitiveactivity. When the brain is activated by any of these conditions, theblood flow and delivery of oxygen to the active regions the tissueoxygen uptake resulting in an increase in blood oxy-hemoglobin (Hb0 ₂)content. The susceptibility difference between diamagneticoxy-hemoglobin and paramagnetic deoxy-hemoglobin (Hb) creates localmagnetic field distortions that affect the processional frequency of thewater protons. The consequential change in magnetic resonance (MR)signal intensity which is proportional to the ratio of Hb0 ₂ to Hb.These signal-intensity alterations related to blood oxygenation aretermed the BOLD (blood oxygenation-level-dependent) effect. The voxelsin paramagnetic Hb content is decreased are illuminated in the image.

While most work on fMRI has been done in humans, it has been difficultto use this technology in conscious animals because of motion artifact.As a result, most studies to date have been limited to animals which aretypically anesthetized in order to minimize this problem of motionartifacts. The low level of arousal during anesthesia either partiallyor completely suppresses the fMRI response and has impeded fMRIapplication to the more physiologically relevant functions that havebeen noted in humans.

Since image resolution is a salient feature of fMRI, precautions toensure improved image quality with minimized head movements areessential. In addition to head movement, it has been observed that anymotion outside the field of view can obscure or mimic changes in signal.

Another, equally significant component for achieving high temporal andspatial image resolution is the generation of radio frequency (RF)magnetic fields. The RF field pulses are transmitted to flip protonsinto the transverse plane of the main direct current (DC) magneticfield. As these protons precess and relax back into the longitudinalplane of the main magnetic field they emit RF magnetic field signals.The electrical assemblies capable of sending and receiving RF signalsare called RF probes, coils, or resonators. Ideally, a RF coil used formagnetic field transmission creates a large homogenous area of protonactivation at a very narrow bandwidth center around the proton resonancefrequency with minimal power requirements. An RF coil used for receivingcovers the largest region of interest within the sample at the highestsignal-to-noise ratio (SNR). RF coils are either volume coils or surfacecoils. A volume coil has the advantage of both sending and receiving RFsignals from large areas of the sample. However, signal-to-noise ratiois compromised because a large spatial domain contributes to the RFsignal, resulting in additional noise and thereby obscuring the RFsignal from the region of interest. A surface coil has the advantage ofimproved SNR due to its close proximity to the sample. Unfortunately, asurface coil is ill suited for RF energy transmission owing to the factthat only a small proton area can be activated. Two criteria are soughtin the design of superior coil performance for high field animalstudies. First, the coils must be as efficient as possible. Transmissionefficiency is increased by reducing the resistive coil losses throughappropriate arrangement of conductors, the use of a shield, and theemployment of low loss dialectric materials. By using a separate surfacecoil in proximity over the desired field of view (FOV) or region ofinterest, the reception efficiency of the acquired NMR signal is furtherincreased. In imaging, spatial and temporal resolutions are proportionalto SNR.

The second criterion to be met for a volume coil, is the uniformity orhomogeneity over a desired FOV in the animal sample. To achieve bothhomogeneity and efficiency for volume coils of Larmor wavelengthdimensions, further improvements are required. Conventionalstate-of-the-art birdcage coil designs will not resonate at thesedimensions.

So-called transversal electromagnetic (TEM) resonator designs have shownpromise for high-frequency, large volume coil applications for humans.However, these TEM designs must be improved upon for the highestfrequency and animal applications allowed by present and future magnets,e.g; for the 9.4T, and the 11.74T, magnets presently being built forlaboratory animal studies.

Increased SNR is sought by making NMR measurements at higher magnetic,or Bo, fields. Main magnetic field strength is, however, only one ofseveral parameters affecting the MR sensitivity. RF coil and tissuelosses can significantly limit the potential SNR gains realized at highfields. SNR (and reciprocal transmission efficiency) will suffer whenthe coil's ohmic resistance, radiation resistance, coupled tissuelosses, RF magnetic field and angular frequency are not optimized.

Tissue losses increasingly impact SNR at higher frequencies. Theseconductive and dielectic losses represented are limited in practice byusing local surface coils, or volume coils efficiently coupled to aregion of interest. In addition to tissue loading, RF losses in thecoils themselves become significant at higher frequencies. The RF coilloss increases with frequency as do the resistive losses in the coil RC,which increases with the square root of the angular frequency, and thelosses from radiation resistance, which increases as at the fourth powerof the angular frequency. The radiation losses also increase as the coilsize increases as S², where S is the area bounded by the coil.

From the above, it is apparent that radiative losses to the sample andenvironment, as well as conductive losses to the load of a coil becomesevere to the point of limiting and eventually degrading the SNR gainsotherwise expected at higher magnetic field strengths. Physically, as acoil is increased in dimension and/or frequency, its electrical circuitlength increases, the coil ceases to behave like a “coil”(RF fieldstorage circuit) and begins to behave more like an “antenna” (RF fieldenergy radiator).

SUMMARY OF THE INVENTION

Applicant's method and apparatus overcomes the difficulties ofperforming fMRI on conscious animals by utilizing a restraining assemblyto eliminate movement artifacts in combination with RF resonator systemto enhance MR signal for mapping changes in brain activity. Therestraining assembly incorporates a coil design including a spatiallyadjustable volume coil for transmitting RF magnetic field pulses and aspatially adjustable dome shaped surface coil for receiving the RFresponse signals from the conscious animal. The significance ofapplicant's method of neuroimaging in conscious animals will changecurrent imagery of the brain from either a static (as seen with mostneurochemical measurements) or a low activation dynamic system in ananesthetized state (as seen with current fMRI or positron emissiontomography (PET) measurements) to more physiologically relevantconditions.

There are two approaches to remedy the problem of high-frequencyradiative losses: 1) construct smaller coils or array elements; and 2)build coils by transmission line or transverse electromagnetic (TEM)principles. Transmission lines eliminate radiative loss. Often it isdesirable to transmit with a larger homogeneous TEM volume coil andreceive with a smaller, closer fitting surface coil. However, to operatea transmitting TEM volume coil in conjunction with a receiving surfacecoil, or an array surface coil, involves switching circuits and anactive tuning/detuning methodology. Thus, the present invention employsa coil mounted on a restraining assembly.

A preferred embodiment of the present invention immobilizes the head andbody of conscious animals for several hours, without compromisingphysiological functions. The apparatus allows for collection of aconsistent voxel by voxel representation of the brain over several dataacquisitions under various experimental conditions. Applicants havedemonstrated fMRI signal changes with high temporal and spatialresolution in discrete brain areas in response to electricalstimulation, such as footshock and during odor stimulation. Changes aremeasured in conscious animals with and without the use of contrastagents. Importantly, the information is obtained without injury to theanimal and provides a method of performing developmental measurements onthe subject over the course of its life.

The single or multi-cylindrical non-magnetic restraining assemblyimmobilizes the head and body of conscious animals for insertion intothe bore of a magnetic resonance (MR) spectrometer.

A restraining assembly according to the invention for imaging consciousanimals includes a head restrainer that restrains the head of theconscious animal, a body restrainer that restrains the body of theanimal, and a frame on which the volume coil is mounted. The framecarries both the head restrainer and the body restrainer and has adamping structure for reducing transmission of movement from the bodyrestrainer to the head restrainer.

In an embodiment of the invention, the multi-cylindrical non-magneticdual-coil animal restrainer to immobilize the head and body of aconscious animal has a cylindrical body restrainer, and a cylindricalhead restrainer that are concentrically mounted within the frame.

The frame can also include an adapter to slide into the bore of the MRspectrometer and adjust the diameter of the frame to the inner diameterof the bore. The frame unit includes a first front-end mounting platehaving an access hole extending through the plate, a second or rear-endmounting plate parallel and spaced from the front-end mounting plate andhaving an access hole extending through the second plate, and aplurality of support members or rods extending between the mountingplates to space and support the mounting plates in relative position,wherein the support rods reduce transmission of movement of the bodyrestrainer to the head restrainer, thereby decoupling vibration betweenthe mounting plates. The support rods also act as rails for sliding andpositioning the cylindrical volume coil over the head and bodyrestrainers.

The body restrainer holds the body of the conscious animal. The bodyrestrainer can include an elongated cylindrical body tube carried by theframe and a shoulder restrainer carried by the cylindrical body tubethat positions of the animal's shoulders once the head restrainer issecured into the front-end mounting plate. The front of the body tubefits into a ring on the backside of the front-end mounting plate. Theseal between the front of the body tube and the ring on the front-endmounting plate is cushioned by a rubber gasket to decouple vibrationbetween the body restrainer and the head restrainer.

The head restrainer immobilizes the head of the conscious animal. Thehead restrainer includes a cylindrical head holder having a bore toreceive and restrain the head of an animal, and a docking post at thefront of the head restrainer for securing the head holder to thefront-end mounting plate.

The head holder restrains the head of the animal to prohibit verticaland horizontal movement of the animal during imaging. The head holderhas a bite bar extending horizontally creating a chord along the bottomof its circular aperture. A vertical nose clamp extends through the topof the head holder and abuts the animal's nose to clamp the animal'smouth thereon.

The animal's head is further restrained by a pair of lateral earclamping elements or screws that extend horizontally through bilateralopenings or the sides of the head holder and a nose clamp that extendsvertically through the head holder. A protective ear piece is placedover the animal's ears and receives the tips of the lateral ear clampingscrews.

A further adaptation of an embodiment includes a restraining jacket torestraining an animal and prohibit limb movement. An animal is placedinto the restraining jacket. Holders for the arms and legs may be usedto further restrict the animal's movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a side perspective of a multi-cylindrical non-magnetic dualcoil restraint system;

FIG. 2 is a side perspective view of the chassis unit;

FIG. 3 is a front view of the front-end mounting plate;

FIG. 4 is a rear perspective view of the chassis unit looking from therear-end mounting plate;

FIG. 5 is a top view of a body tube of the body restraining unit;

FIG. 6 is a side perspective view of the body tube and a shoulderbracket of the body restraining unit;

FIG. 7A is a front perspective view of the cylindrical head holder;

FIG. 7B is a side view of the head holder;

FIG. 7C is a perspective view of the assembled dual coil and restrainersystem;

FIG. 8 is a schematic of the overall MRI system;

FIG. 9 is a schematic of the interface between the RF-coils and MRItransmit/receive system.

FIG. 10A is a exploded perspective view of a volume coil;

FIG. 10B illustrates the slotted volume coil;

FIG. 11A is a view of the inner surface of a printed circuit board;

FIG. 11B is a view of the inner surface of a printed circuit board;

FIG. 12 is a schematic of circuitry associated with the volume coil;

FIG. 13 is a schematic of circuitry system on the volume coil;

FIG. 14 is a schematic representation of circuitry associated of thevolume coil;

FIG. 15A is a schematic of the conductor circuitry of the volume coil;

FIG. 15B is a schematic of interrelation of several of the strip ofshielding;

FIG. 16A is a view of a single loop surface coil;

FIG. 16B is a is a schematic circuit of a single loop surface coil;

FIG. 17A is a view of a dome shape surface coil;

FIG. 17B is a schematic of circuitry of a dome surface coil;

FIG. 18 is a front perspective view of a rat with the semi-circular earpiece;

FIG. 19 is a side view of a rat with the semi-circular ear piece;

FIG. 20 is a side view of a rat in the cylindrical head holder;

FIG. 21 is a front view of a rat in the cylindrical head holder;

FIG. 22 is a view of the restraining jacket;

FIG. 23 is a side view of a rat in the assembled fMRI restraint;

FIGS. 24A-24D illustrate head restrainer, support frame and surface coilcomponents of a preferred embodiment of the inventions.

FIG. 25 shows nine contiguous anatomical sections take prior to andsixty minutes following hemorrhagic stroke;

FIG. 26 shows images collected at 30 second intervals over an 8 minuteperiod showing changes in BOLD signal with hemorrhagic stroke in aconscious animal;

FIG. 27 shows images collected at 30 second intervals over an 8 minuteperiod showing changes in BOLD signal for a non-stroke conscious animal;

FIG. 28 shows a sequence of graphical illustration of BOLD signal as afunction of time.

FIGS. 29A and 29B are front and side perspective views of an adjustableembodiment of the front-end mounting plate; and

FIG. 30 is a perspective view of the adjustable mounting assembly.

DETAILED DESCRIPTION OF THE INVENTION

In the figures, like numbers are used to indicate like elements. FIG. 1shows a multi-cylindrical, dual-coil animal restrainer 30 according tothe invention. The multi-cylindrical, dual-coil animal restrainer 30including a volume coil 32 and a surface coil 34, as seen in FIG. 8A,and the method described allow the functional magnetic resonance imaging(fMRI) of conscious animals.

Referring to FIG. 1, the multi-cylindrical, dual-coil animal restrainer30 has the volume coil 32, which will be described further below ingreater detail, and a restraining assembly 36. The restraining assembly36 includes a support frame or chassis 38, a head retainer 40, and abody retainer 42.

The frame 38 is shown in perspective in FIG. 2. The frame 38 has a firstor front-end mounting plate 46 and a second or rear-end mounting plate48 spaced apart by a plurality of support members or rods 50. Thefront-end mounting plate 46 has a hole 52 which is collinear with alongitudinal axis 54 of the frame 38. The rear-end mounting plate 48also has a cylindrical opening 56 which is collinear with thelongitudinal axis 54. The cylindrical opening 56 of rear-end mountingplate 48 is larger than the hole 52 on the front-end mounting plate forthe reasons set forth below. In addition, both the mounting plates 46and 48 have threaded openings 58 which can receive an adjustablefastening post for centering and securing the frame 38 within a cavityor bore of a magnetic resonance MR spectrometer.

The bore 212, as shown in FIG. 8, is used in MR spectrometers used forfunctional imaging range from 10 cm to 100 cm. Human MR spectrometersrange between 70-100 cm in diameter while a majority of the animal MRspectrometers used for functional imaging range from 10-50 cm. Thefront- and rear-end mounting plates can be made to fit any internal borediameter in this range. Hence the multi-cylindrical dual coil animalrestrainer can be used in both full body human spectrometers anddedicated smaller bore animal spectrometers.

The support rods 50 position the front-end and rear-end mounting plates46 and 48 relative to each other and maintain the planes of the platesparallel to each other and perpendicular to the longitudinal axis 54. Inaddition, the support rods 50 are of such a size and materialcharacteristics that the minor movement of the rear-end mounting plate48 would not affect movement into the front-end mounting plate 46.

In one embodiment, the support rods 50 are connected to the mountingplates 46 and 48 by a damping mechanism such as rubber gaskets tofurther reduce transmission of movement caused on the rear-end mountingplate 48 to propagate to the front-end mounting plate 46.

The front-end mounting plate receives a docking post 64 which is part ofthe head retainer 40, as explained in further detail below. In anembodiment, the entire mounting unit is formed of a non-metallictransparent material such as Plexiglass™ or Nylon to minimize theinfluence on the magnetic fields.

Referring to FIG. 3, the front view of the front-end frame plate 46 isshown. The support rods 50 are extending through the mounting plate 46.In addition, in that the mounting plate 46 is transparent, thepositioning tube 64 can be seen.

Referring to FIG. 4, a rear perspective view of the mounting unit 38 isseen. The rear-end mounting plate 48 has the cylindrical opening 56which is surrounded by the support rods 50 that extend parallel to andspaced from the longitudinal axis 54 of the frame. The support rodsextend to the front-end mounting plate 46. The front-end mounting plate46 has the hole 52 surrounded by a positioning tube 64. Encircling thepositioning tube 64 is an annular groove 66 defined by the positioningtube 64 and an annular ring 68. In an embodiment, the annular groove 66receives a resilient gasket 70 to improve dampening of motion asexplained in further detail below.

Referring to FIG. 5, the body retainer 42 has a body tube 74 which in apreferred embodiment, is Plexiglass™. The tube 74 has a cylindrical thinwall section 76 and a flange 78 for securing to the rear-end mountingplate 48. The thin wall section 76 has a cut-out portion 80, as seen inFIG. 6, which allows access to the head restraining unit 40. Inaddition, there is a slot 82 and an opening 84 into the cut-out portion80 to prevent coupling of the body retainer 42 with the head retainer40, as explained in further detail below.

Still referring to FIG. 6, the body retainer 42 also has a shoulderholder 86. The shoulder holder 86 is retained on the thin wall section76 by a plurality of fasteners 88 received in slots 90 on the thin wallsection 76.

The shoulder holder 86 limits movement of the shoulder of the animaltoward the head retainer 40. In an alternative, the shoulder of ananimal can be a pair of pins 92 as shown in phantom which drop intoholes in the thin wall section 76 of the body tube. The choice of theshoulder holder 86 or the pins 92 is dependent on several factorsincluding the size and type of animal to be restrained.

Referring to FIG. 7A, the head retainer 40 has a head holder 94 and theposition tube 64, as seen in FIG. 2. The head holder 94 has a bore 96which receives the head of the animal. The head is received from theother end of the head holder 94 from that shown in FIG. 7A. An aperture98 extends from the bore 96 to communicate with an aperture 100 in theposition tube 64 as seen in FIG. 4.

A pair of flanges 102 extend outward on the head holder 94 to encirclethe position tube 64. Each of the flanges 102 have a slot 104 to accepta fastener 106, as seen in FIG. 4, to secure the head holder 94 to theposition tube 64 of the head restrainer 40.

The head holder 94 has a bite bar 108 extending horizontally along achord of the circular aperture 98 to provide a rest for the upper jaw ofa restrained animal. Mounted through the top of the cylindrical headholder is a nose clamping screw 110 with a nose bar to secure the noseof a restrained animal to the bite bar 108. A pair of opposed lateralscrew slots 112 are located in the sides of the cylindrical head holder94 to receive lateral ear clamping screws 114, as seen in FIG. 7B.

The lateral ear clamping screw 114 has a washer shown in hidden line.The lateral ear clamping screws 114 are used to position the animallateral in the head holder 94. In addition the head holder 94 has a pairof lower jaw screws 116 for restraining the lower jaw of the animal.

The head holder 94 also has a hole 118 for receiving a post 198 carriedon the surface coil 34, as seen in FIG. 15A, to position the surfacecoil 34.

The surface coil 34, which is received in the bore 96 of the head holder94 of the head restrained unit 40, works in conjunction with the volumecoil 32 and a system operating controller 200 to produce the image.Referring to FIG. 8, a schematic of an embodiment of the inventor isshown for using an MRI system to perform neuroimaging of animals. Aconventional MRI device 210 for use with animals has a tunnel bore 212in generally a range of 15 to 24 centimeters in diameter. A main magnet214 and a gradient coil set 216 encircle the tunnel bore 212 as is knownin the art.

The multi-cylindrical, dual-coil animal restrainer 30 including therestraining assembly 36 and the volume coil 32 and surface coil 34 areinstalled into the tunnel bore 212. The volume coil 32 is capable movingalong the support rods 50 of the frame 38 as explained in further detailbelow. Both the surface coil 34 and the volume coil 32 are connected viawiring which extends out of the tunnel bore 212 to a transceiver unit220 of the system operating controller 200 as explained in furtherdetail with respect to FIG.9. In one embodiment, the volume coil 32transmits and the surface coil 34 is used for receiving. In otherembodiments the surface coil both transmits and receives or the volumecoil transmits and receives.

The image processing can be performed off-line on a 100 MHZ HP Apollo735 workstation using IDL imaging software, Version 4.0 and analyzed ona Power Mac 60/66 using NIH imaging software, Version 1.56 (AppleComputer, Inc., Cupertino, Calif.). The stimulated and baseline imageswere subtracted to reveal regions of activation. The region of greatestactivation was determined from the subtraction image. The correspondingregion of the baseline and stimulated data sets were demarcated and therelative signal intensity was calculated on a pixel-by-pixel basis.

Referring to FIG. 9, a schematic of the interface between the RF coils32 and 34 and a MRI transmit/receive system 218. Both the TEM volumecoil 32 and the surface coil 34 is connected to a transceiver unit 220.The transceiver unit 220 has an RF transmitter 234, an RF receiver 226and a system controller 228. The system controller 228 controls a pairof switching circuits 230 to transmit and receive the signal from theproper coil 32 or 34. In addition, the system controller 228 also cancontrol an interface 230 to provide active tuning/detuning of the coils.For instance, if the TEM volume coil 32, also referred to as the bodycoil, is active, transmitting RF energy to the animal, the surface coil34 is detuned in order to avoid interference. Conversely, when thesurface coil 34 is receiving the MR signal from the animal, the TEMvolume coil 32 is detuned.

Referring to FIG. 10A, an exploded perspective view of the volume coil32 is shown with the core shown in three segments. The volume coil 32has a cylindrical non-metal core module 120. The core module 120 has acylindrical bore 122 that extends through the core module 120 along alongitudinal axis 124. The cylindrical bore 122 defines an inner surface126. In addition, the core module 120 has a plurality of bores 128extending through the annular core module 120 parallel to and spacedfrom the longitudinal axis 124. The apertures 128 accept the supportrods 50 to allow the volume coil 32 to move relative to the restrainingassembly 36. The volume coil 32 has a plurality of conductive striplines 130 extending parallel to the longitudinal axis 124 on the innersurface 126 of the core module 120.

The volume coil 32 has a pair of printed circuit boards (PCB) 134mounted on the outer, side edges of the core module 120. In addition,the volume coil 32 has shielding 136 which overlies the core module 120as seen in FIG. 10B. The shielding 136 is formed in strips to reduce theoccurrence of eddy currents induced by the gradient coils 216, as seenin FIG. 8.

The shielding 136 in strips forms a plurality of coaxial slots 137 alongthe coil's length which serve to interrupt switched gradient inducededdy propagation. Reactively bridged azimuthal slots can extend aroundthe TEM coil's outer wall, end walls, and inner “wall” further limiteddies, and extend the coil's frequency band and dimensional options.

In addition to the shielding 136 being strips, the conductive striplines 130 creates slots 137 that interrupt eddy current propagation inthe TEM coil divide the TEM cavity wall, front to back. The innerelements can be flat, copper foil double-sided strip-line elements,split coaxial elements, or single line copper conductors. FIGS. 10A and10B shows copper foil strip line elements for strip lines 130. Thissegmented TEM coil combines the internal line element 130 with theexternal cavity segment, the shielding 136, forming a resonance circuit.Each functional element can be sub-divided capacitively into one throughfour or more segments. Trimmer capacitors 139 on the outside wall of theFIG. 10B coil depict one such division. As in a simple surface coil, thenumber of capacitive divisions in each resonant unit can be chosen to befew when a more inductive, lower frequency performance of the TEM coilis desired. In contrast, each unit can be divided four or more times toaffect the resonance frequency of this slotted TEM volume coil. Therebyelectrically modified, the B₁ field generated by this subdivided coilwill have improved field linearity and homogeneity.

The printed circuit board 134 shown in FIG. 11A is an exposed surface138, the surface of which faces away from the core module 120 of thevolume coil 32. While FIG. 11B shows the inner surface, the surfacewhich faces the core module 120. The inner surface which is covered withand is part of the shielding along with strips of shielding 136 shown inFIGS. 10A and 10B. The printed circuit board 134 has a plurality ofcomponents which are discussed with respect to FIGS. 12-15B.

A schematic of circuitry associated with the volume coil 32 is shown inFIG. 12. The volume coil 32 has a plurality of resonating elements 146which include the strip lines 130 and the shielding 136. The elements146 represented as number 1 and number 12 of a twelve element volumecoil 32 are shown. It is recognized that the TEM volume coil 32 can havemore or less elements 146, such as 8 or 16. The resonating elements 146are connected to a detuning/tuning circuits 156 in order to move theresonance frequency of the resonating elements 146 away from the targetresonance so as not to interfere with the receiving coil as explained infurther detail below. The volume coil 32 in addition has a matchingcircuit 172 for adjusting the impedance of the resonating element 146 tothat of the RF source. The TEM volume coil 32 is shown in FIG. 12 withthe transceiver unit 220 and a detuning source 142 associated with itscircuitry. The RF source 140, the transceiver unit 220 and the detuningsource, 142, however, are not part of and are located remote from thevolume coil 32 and are connected through coaxial cables which extend outof the cavity 212 and connect to the transceiver unit 220, as seen inFIG. 8. The volume coil 32 has an RF decoupling circuit 190. The RFdecoupling circuit 128 ensures that the DC detuning signal does notinterfere with the RF signal path.

FIG. 13 shows a more detail view of circuitry associated with the volumecoil 32 located on the volume coil 32. The matching circuit 172 includesa variable tunable capacitor 174. The detuning source 142 is connectedto the detuning circuit 156 via a filter circuit 164 and the RFdecoupling circuit 178. The filter circuit 164 has a pair of inductors180 and a capacitor 182. The filter 164 is for separating the highfrequency RF from interfering with the tuning/detuning signal. The RFdecoupling circuit 178 has three radio-frequency chokes (RFC) 184 whichrepresent low resistance to the DC current, but high impedance to the RFsignal, thereby decoupling both signals from each other. From thedetuning circuit 156 which contains a pair of pin diodes 158 and 160,the resonating element 146 is connected.

FIG. 14 shows additional elements of the circuitry of volume coil 32. Asindicated above, the volume coil 32 has several inputs including the RFsource 140 from the RF transmitter 224 of the transceiver unit 220, theDC source 142 and a ground 144. The strip lines 130 are each part of aresonating element 146. The strip lines 130 are represented in thecircuit as distributed inductor 148 in the resonating element 146. Thestrip lines 130, as represented by the inductors 148, are connected inseries to a pair of capacitors 150 and 152. One of the capacitors is thevariable, tuneable capacitor 152. In the embodiment shown in FIG. 14,the variable, tuneable capacitors 152 of one of the resonating element146 is located on the front PCB 134 and the variable, tuneablecapacitors 152 of the adjacent resonating elements 146 are located onthe rear PCB 134; in that there are an even number of resonatingelements 146, the variable, tuneable capacitors 152 are equally locatedon the front PCB and the rear PCB. The other capacitor, the capacitor150, for each resonating element 146 is located on the other PCB 134than that of the variable, tuneable capacitor 152.

In an alternative embodiment, all the variable, tuneable capacitors 152of the resonating elements 146 are located on the front PCB 134. Theother capacitor, the capacitor 150 is located on the rear PCB 134.

The front PCB 134 is represented by boxes 190 in FIG. 14 and the rearPCB 134 is represented by boxes 192. The stripes of shielding 136 arerepresented by a distributed inductor. The variable, tuneable capacitors152 can be tuned manually or electronically. The capacitors 150 and 152are each carried on the printed circuit board 134. One of the sets ofthe capacitors 150 and 152 and a strip line 130 in conjunction with theouter strip shielding 136 form an element which is connected to thedetuning circuit 156.

Each of the detuning circuits 156 has a pair of diodes 158 and 160. Inone embodiment, the diodes 158 and 160 are pin diodes. The RF decouplingcircuit 178 has a plurality of inductors 162 (184). One of the detuningcircuits 156 and one of the decoupling circuits 178 are each interposedbetween one of the resonating elements 146 and the filter circuit 164.

The filter 164 is connected to the DC source 142 through a resistor 170.The DC source 142 is used in operating the circuit in conjunction withsurface coil 34 as explained below.

Still referring to FIG. 14, the RF source 140 and the matching circuit172 are connected to one of the resonating element 146. The matchingcircuit 172 includes the variable tuneable capacitor 174 which is tunedmanually.

Referring to FIG. 15A, a portion of the volume coil 32 is represented.In the embodiment represented in FIG. 15A, twelve elements are locatedon the volume coil 32. The strip lines 130 are represented bydistributed inductors. Connected to the strip line 130 is a pair ofcapacitors in the series 150 and 152 wherein one of the capacitors 152is a variable tuneable capacitor. In the embodiment shown in FIG. 15A,the variable, tunable capacitors 152 is shown alternating from being onthe front printed circuit board 134 to being on the rear printed circuitboard 134 for every other resonating element. In addition, each elementshows the shielding 136 which is the return path for the respected stripline 130. The adjacent strip lines 130 are mutually coupled.

As indicated above, the volume coil 32 has shielding 136 located on theouter surface of the core module 120. The strips of shielding 136 areconnected to each other by capacitors located at alternative ends of thestrips of shielding 136. The capacitors 186 are located on the outersurface of the resonating element as part of the shielding 136.Additional capacitors may be located at the other end of the strips ofshielding 136 or alternatively they may be shorted in an effort toreduce the occurrence of eddy currents due to the activation of thegradient coils. The first element shown connected to a detuning circuit.

A schematic showing the connection of adjacent strips of shielding 136for a portion of the volume coil 32 is seen in FIG. 15B. The strips ofshielding 136 are connected to each other by capacitors located on theouter surface of the resonating element as part of the shielding such asseen in FIG. 10B. The capacitors are located at alternative ends of thestrips of shielding 136. In the embodiment shown, the other end of thestrips of shielding 136 are shorted to reduce the occurrence of eddycurrents as discussed above.

Working with the volume coil 32 is the surface coil 34 that can be usedin one mode to receive the MR signal from the animal. In another mode,the surface coil 34 both transmits and receives the RF.

The surface coil 32 can take various shapes. The surface coil 32 canhave a single loop as described with respect to FIGS. 16A-16B or havemultiple loops arranged in a dome shaped surface coil 196 as seen inFIGS. 17A and 17B.

Referring to FIGS. 16A and 16B, a surface coil 32 with a single loop isshown. The circuitry of the surface coil of FIG. 16A is shown in FIG.16B. The resonating element 192 of the single loop has a pair ofmetallic strips with interposed capacitors schematically shown in FIG.16B. The single loop surface coil has a detuning circuit 193 and adecoupling circuit 194.

The single loop surface coil 34 has a connection to the transceiver andthe detuning source. The single loop surface coil 34 has a post 198 forattaching to the head holder 94 or other device as explained below.

An alternative to the single loop surface coil 34 of FIGS. 16A and 16Bis a multiple loop dome shaped surface coil device 252 shown in FIG.17A. FIG. 17B is a schematic of the multiple loop surface coil 196 ofthe dome shaped device 252.

The surface coil 196 has a post 198 as seen in FIG. 17A for attaching tothe head holder 94 or other device as explained below. The surface coil196 a pair of connectors 204 and 206 which are connected to the RFsource 140 and the DC source 142. Similar to the volume coil 32, thesurface coil 196 has a detuning circuit 234 and matching capacitorcircuit 236. Also similar to volume coil 32, the surface coil 196 hasthe inputs of the RS source 140, the DC source 142 and the ground 144.

The surface coil 196 has a plurality of resonating elements 226 eachwith a strip line which is represented by an inductor. Both fixed andtuneable capacitors are deployed. The tuneable capacitor is used toadjust the resonance frequency with a capacitor is used to match thecircuit.

With the multi-cylindrical, dual-coil animal restrainer 30 including thevolume coil 32 and the surface coil 34 described, a method of performingneuroimaging is described.

The animal 260 is lightly anesthetized prior to insertion into therestraining system 30. As shown in FIGS. 18, and 19, a semi-circular earpiece 262 is fitted over the head 264 of the animal 260 whereupon theanimal's head 264 is placed into head holder 94.

Referring to FIGS. 20 and 21, lateral ear clamping screws 114 areinserted through the pair of lateral screw slots 112 and tightenedagainst divots in a semi-circular ear piece 262 to prevent the animal260 from moving horizontally. The upper jaw of the animal 260, such as amonkey, is fitted over the bite bar 108 and nose clamping screw 110 istightened against the snout of the animal to secure it to the bite bar108 and thereby eliminate vertical movement maintaining a stereotaxicposition of the animal's head.

FIG. 22 shows a restraining jacket 268 used to restrain the animal 260.The jacket 268 is made of a looped lined, such as marketed under thename Velcro™, non-flexible fabric with a hooked closure 270, such asmarketed under the name Velcro™. The restraining jacket 268 has a pairof arm holders 272 and a pair of leg holders 274 for further restrictthe animal's movement. The jacket 268 has holes for the animal's headand rear/tail 276 and 278, respectively.

Referring to FIG. 23, with the head of the animal 260 retained in thehead holder 94, as shown in FIG. 20 and 21, and the body of the animalin the retraining jacket 268, the head holder 94 is fixedly mounted tothe position tube 64 by a pair of fasteners 106. The pair of flanges orlips 102 extend outward on the head holder 94 to encircle the positiontube 64. Each of the flanges 102 have a slot 104 to accept the fastener106. The position tube 64 is received with a gasket 70 interposed.

With the head retraining unit 40 attached to the mounting unit 38, thebody tube 74 of the body restraining unit 42 is slipped through thecylindrical opening 56 of the rear-end mounting plate 48 and receivesthe body of the animal 260 in the restraining jacket 268. The shoulderholder 86 or pins 92 are installed limits movement of the shoulder ofthe animal toward the head restraining unit 40.

The surface coil 34 is installed into the head restraint 40 prior to theinstallation of the head 264 of the animal 260 and lowered into positionafter the animal is in position in the body tube 74 and the headrestraining unit 40. The volume coil 32 is slid along the support rods50 to the proper position encircling the animal 260.

The multi-cylindrical, dual-coil animal restrainer 30 is installed intothe tunnel bore 212 of the MRI device 210. Before testing the anesthesiahas worn off so that the animal is conscious. The MRI transmit/receivesystem 242 controlling the surface coil 34 and the volume coil 32.

FIG. 24A shows a nose clamp 240 and different size ear caps for rodents.FIG. 24B shows the head restrainer 250 mounted within the support fromdescribed previously. FIG. 24C and 24D show a head restrainer 250 thatcan be used with a rodent, for example, with the nose clamp 240extending to the bite bar. These figures also show the dome coil 252 ofFIG. 17A mounted with the head restrainer.

The following are examples of the use of the apparatus for variousapplications.

The first example uses magnetic resonance imaging with T2* weightedtechnique to identify the site and neuropathology of acute intracranialhemorrhage. T2* weighted technique is used to image the onset andprogression of a spontaneous hemorrhagic stroke in conscious rats. Thisallows researchers to have an animal model and method using MRIaccording to this invention to study the physiology of hemorrhagicstroke in real-time.

MRI data were acquired using a Bruker Biospec DBX 4.7/40 (4.7 Tesla, 40cm bore Bruker Medical, Inc., Billerica, Mass.) animal MRI/MRSspectrometer using a 15 cm actively shielded gradient inset. Animalsbetween the ages of 12-14 weeks were lightly anesthetized with sodiumpentobarbital (25 mg/kg) and fit into the restraining assembly 36according to the invention. The tail vein was catheterized for theinjection of norepinephrine. Functional imaging began no less than 90min after recovery from anesthesia.

At the beginning of each session, a fast scout (GEFI) imaging sequenceof three orthogonal views was used to make sure of the brainorientation. Afterwards, a high quality, proton weighted, spin echoanatomical data set was collected with the following parameters:isotropic 4.8 cm FOV and 256 matrix, 0.187 mm pixel, TR 2000, TE=31msec, 18 slices, 8.5 minute imaging time. Functional images wereobtained using an interleaved T2*-weighted EPI spin echo sequence(256×256, using 16 interleaves) with the same spatial parameters andresolution, but with ten slices, TR=1800, TE=48 msec. The ten coronalslices were acquired every 30 seconds. The sequence was repeated 24times for a total of 240 images. The first 10 repetitions were baselinedata followed by norepinephrine injection.

The results of the proton weighted images is discussed followed by theT2′ weighted images. Nine contiguous anatomical sections taken prior toand sixty-min following hemorrhagic stroke are shown in FIG. 25.Intracranial hemorrhage caused a dramatic change in proton weightedimage contrast. The most obvious morphological change is the exaggeratedexpansion of the ventricular system highlighted by hypointense signal.In contrast, the parenchyma adjacent to the ventricles is hyperintense.Indeed, one hr after hemorrhagic stroke, the brain shows greater MRsignal throughout the parenchyma as compared to the pre strokecondition. From these data it would appear that the stroke occurred inthe dorsomedial caudate/putamen adjacent to the lateral ventricle andcorpus callosum as shown in FIG. 25, section E.

Images collected at 30 second intervals over an 8 minute period showingchanges in BOLD signal with hemorrhagic stroke in a conscious animal arepresented in FIG. 26. Stroke was precipitated by the tail vein injectionof a hypertensive dose of norepinephine given during data acquisition.The data presented are from the coronal section shown in FIG. 25,section E. Positive (red voxels) and negative (yellow and black voxels)changes in BOLD signal are mapped over the raw data image. Data from aSPSH rat that did not stroke in response to the tail-vein injection ofnorepinephrine is shown in FIG. 27.

Thirty seconds after injection of norepinephrine there was a robustincrease in BOLD signal over the cerebral cortex in the stroke animal.This increase was accompanied by an equally robust but opposite decreasein BOLD signal in the basal areas of the brain, particularly in thecontralateral amygdaloid complex, piriform and perirhinal cortices.These changes in BOLD signal in the first 30 sec followingnorepinephrine injection corresponds in time with the peak change inblood pressure observed in studies outside the magnet. By one min thedecreased BOLD signal was primarily confined to midline thalamic nuclei,while enhanced BOLD signal was more widely but diffusely spread aroundthe brain. Between 60-90 sec after injection there is a decrease in BOLDsignal in excess of 60% (black voxels) that appears at the dorsomedialcaudate/putamen and third ventricle. The caudate/putamen is the putativesite of intracranial hemorrhage. There appears to be a unilateralincrease in BOLD signal throughout the striatum on the side of thestroke. Over the course of the next five-min most of the changes in BOLDsignal are lateralized to the side of the stroke. However, theamygdaloid complex and piriform cortex shows bilateral activity. Overthe course of the study, the striatum expands into a larger area ofdecreased BOLD signal adjacent to voxels showing increased BOLD signal.This checkerboard pattern where one voxel shows increase in BOLD signaland its adjacent voxel shows decrease in signal is more prevalent as thestroke progresses. The animal was removed from the magnet following thecollection of the last proton weighted data set (FIG. 25) approximately60 min after the initiation of stroke. The animal was conscious andshowed normal motor activity when returned to its home cage. However,over the next ninety min the animal's conditioned deteriorated leadingto death. Gross histology revealed clotted blood throughout thesubarachnoid space over the cerebral hemispheres. The ventricles weredistended and filled with blood.

A time series at approximately the same coronal plain in a SPSH rat thatdid not stroke following injection of norepinephrine is shown in FIG.27. Similar data were collected for the other two animals that failed tostroke during imaging. The cortices and basal ganglia showed noostensible changes in BOLD signal during the 3-4 min hypertensiveepisode following injection of norepinephrine. The hypothalamus,particularly the paraventricular and supraoptic nuclei of thehypothalamus showed a sustained increase in BOLD signal. There were nolocalized, sustained hypointense signals that would indicateintracranial bleeding. This was confirmed by subsequent immunostainingfor fibrinogen that revealed no signs of vascular hemorrhage.

The following example relates to using high field MRI to study cocaineaddiction in monkeys. Changes in functional activity are observed duringcocaine self-administration, withdrawal and reinstatement, i.e.,“craving” elicited by the presentation of conditioned cues duringmagnetic resonance imaging (MRI) in conscious rhesus monkeys. With MRIit is possible to follow brain development, function and chemistry ofnon-human primates over their lifetime with exceptional spatial andtemporal resolution. Therein allowing non-invasive developmental studiesto identify changes in neural circuits involved in drug addiction,extinction and reinstatement.

The restraining assembly 36 was sized to fit a 4 kg rhesus (young adult)into a operant/restrainer designed for a 24 cm tunnel bore 212 of an MRIdevice 210. The restraining assembly 36 with RF electronics includingthe volume coil 32 and the dome shaped surface coil 196 discussed aboveis used with a train rhesus monkeys to self-administer cocaine duringimaging in a 9.4 T spectrometer.

The rhesus monkeys are habituated for 6-8 wk to the operant/restrainerin a simulated “magnet” environment. Under general anesthesia, animalsare implanted with chronic intravenous catheters. Over the followingthree months, animals are trained to self-administer cocaine to a secondorder fixed interval schedule in the operant/restrainer in the simulatedenvironment. Prior to imaging, animals are habituated for two weeks tothe movement and placement of the restrainer into the magnet. Actuallyimaging is begun when animals show the same level of cocaineadministration in the magnet as they do outside. The animals are imagedduring three separate trials (days) of cocaine-self administration.These daily trials characterize the direct pharmacological effects ofcocaine for comparison with extinction and reinstatement effects.Extinction trials follow self-administration. Over several days, animalsbar press for the injection of saline without the conditioned stimulus(red light). This extinction protocol takes about one week and leads tothe diminution of bar pressing. Animals are imaged each day ofextinction trials. Presentation of the conditioned stimulus is reinstatebar pressing, a situation analogous to cocaine craving. Reinstatementbehavior is most pronounced during the first 2-3 daily trials butquickly wanes thereafter. Animals are imaged during each dailyreinstatement trial.

This example is done with the background that cocaine addiction is anational health problem with over three million cocaine abusers in needof treatment. Cocaine addition can take years to develop following firstexposure and many more to treat. While the physiological effects ofcocaine withdrawal are not as apparent as those for alcohol andbarbiturates there is a pattern of symptoms characteristic of cocaineabstinence. Immediately after cessation of drug use there is “crash” ofmood with behavioral symptoms of depression, agitation, anxiety andcocaine craving. This period is followed by several weeks of withdrawalcharacterized by prolonged dysphoria and intense cocaine cravingassociated with memories of drug-induced euphoria. This period ofwithdrawal is particularly sensitive to environmental stimuli that theaddict associates with drug use. These environmental stimuli orconditioned cues intensify cocaine craving. Following withdrawal, thereis lasting cocaine abstinence or extinction. However, conditioned cuescan still elicit cocaine craving many years after the last cocaine useand trigger a relapse into drug abuse. A key to understanding cocainerelapse is identifying neural pathways in the brain contributing tocue-evoked craving.

Although cocaine abuse is a human problem, many of the questionsinvolving the neurobiological mechanisms contributing to craving andrelapse are more easily studied and manipulated in non-human primates.Indeed, squirrel monkeys and more recently rhesus monkeys have been usedfor many years to study cocaine abuse. These animals can readily betrained to self-administer cocaine in a classical conditioning paradigmmaking them amenable to studying cocaine reinforcement, extinction andconditioned reinstatement (craving is a term applied to humans whilereinstatement is a more objective term applied to animals). Similarprospective studies establishing addiction, extinction and craving arenot possible in human subjects. The problems of spatial resolution,motion artifact and prospective experimental designs are resolved byimaging awake monkeys at ultra-high magnetic field strengths inrestraining assembly 36 of the invention. Indeed, functional imaging innon-human primates with a 9.4 T MR spectrometer provides a spatialresolution of 2 mm³ with multi-slice acquisitions in seconds. This levelof anatomical resolution with temporal windows of seconds would allowthe sequential activation of neural circuits associated withself-administration, extinction and reinstatement in exquisite detail.

A less powerful system would not work. For example, the amygdala an areaidentified in cocaine craving has over twenty different nuclei andsubnuclei 18, 67 that can be divided into the corticomedial andbasolateral areas. The nuclei associated with the basolateral amygdalaare involved in avoidance learning, stimulus-reward associations andprocessing of temporal and sequential information. Many of these areashave anatomical boundaries of mm³ or less and would not be resolved in a1.5 T spectrometer or even in the newer 3.0 and 4.0 T systems.

While work on this example is not complete as a filing, it is expectedthat it will characterize changes in CNS activity during intravenouscocaine self-administration in rhesus monkeys. In addition, experimentswill investigate the ability of environmental stimuli associated withdrug-administration to alter CNS function in the absence of cocaine. Itis anticipated that presentation of drug-paired stimuli in the absenceof cocaine administration will induce a pattern of activation thatdiffers from that induced directly by cocaine. The activation ofparalimbic and limbic structures associated with learning and emotionappear critical for cocaine craving and relapse triggered byenvironmental cues. Understanding the activation and integration ofthese neural pathways in cue-elicited craving may help in the design oftherapeutics and potential psychosocial intervention strategies.Functional MRI in ultra-high magnetic field strengths is non-invasiveand provides superior spatial and temporal resolution using theapparatus and method of this invention will help identify discretenuclei within brain regions postulated to be involved in cocaine abuse.

Any minor head movement can distort the image and may also create achange in signal intensity that can be mistaken for stimulus-associatedchanges in brain activity. In addition to head movement, motion outsidethe field of view can also obscure or mimic the signal from neuronalactivation. Unfortunately, the use of anesthesia precludes any studiesthat require emotional and cognitive activities. For example, it wouldnot be possible to study the emotional and cognitive componentscontributing to cue-induced reinstatement of cocaine self-administrationin monkeys. The multi-cylindrical, dual-coil animal restrainer 30reduces motion artifact while still allowing the use of anon-anesthetized animal.

With the monkey under light ketamine anesthesia, the animal is fit intothe head restraining unit 40 with a built in surface coil 34. Theplastic semicircular headpiece 262 with blunted ear supports that fitinto the ear canals is position over the ears, similar to that shown inFIGS. 18 and 19 with the rat. The head 264 is placed into thecylindrical head holder with the animal's canines secured over a bitebar 108 and ears positioned inside the head holder with adjustablescrews, the lateral ear clamping screw 114, fitted into lateral slots112. The head holder 94 is secured to a center post, the position tube64, at the front of the chassis and secured to the front-end mountingplate 64. In this design it is easier for the researcher to position thehead of the animal into the head restrainer before connecting to thechassis. The body of the animal is placed into the body tube 74. Thebody tube 74 “floats” down the center of the chassis connecting at thefront and rear-end plates and buffered by rubber gaskets. As indicatedabove, the restraining assembly 36 isolates all of the body movementfrom the head restrainer unit 40 and RF electronics and minimizes motionartifact. The body restraining unit 42 including the body tube 74 isdesigned to allow for unrestricted respiration with minimal movement.Once the animal is positioned in the body restraining unit 42, thevolume coil 32 is slide over the head restrainer unit 40 and locked intoplace.

The volume coil 32, the surface coil 34 and head restrainer unit 40 forthe rhesus monkey in a 24 cm bore gradient set are similar to thosediscussed above. The volume coil 32 has in one embodiment 16 elements incontrast to the 12 elements discussed above.

It is recognized that the monkeys need to be acclimated toimmobilization stress. The stress caused by immobilization and noisefrom the MR scanner during functional imaging in fully conscious animalsis a major concern. While motion artifact has been eliminated orminimized with animal restraining devices, the confounding variable ofstress would at first glance limit the number of experimentalapplications and cloud the interpretation of data. As animals can beadapted to the imaging procedure as measured by basal levels of stresshormones and resting levels of autonomic activity, then it is possibleto isolate the stress-mediated changes in brain activity from those ofinterest.

-   Step 1. A prototype two-part chassis is constructed of nylon to fit    into the 24 cm bore of the gradient set. This basic two-part system    has the advantage of separating the head restrainer and RF    electronics from the rest of the body restrainer minimizing motion    artifact caused by body movement. A lightly anesthetized rhesus    monkey is placed into the body restrainer with its head secured into    the head holder containing the phase array surface coil. This unit    is connected with two screw rods into the front chassis. The head    restrainer is locked into a support post on the front chassis. The    TEM volume coil slides along rails extending from the front chassis    and positioned surrounding the head restrainer. Once positioned in    the magnet the two screw rods will be backed off freeing and    isolating the front and back components.-   Step 2. Three young adult rhesus monkeys (4.0 to 5.0 kg) are    anesthetized with ketamine and used for head and body measurements.    The dimensions of the head will determine the minimum internal    diameter of the head holder on which the surface and volume coils    must be adapted. The distance of the external auditory meatus to the    surface of the skull is measured to determine the position of the    adjustable screws in the lateral sleeves along the circumference of    the head restrainer. This is necessary to position the head in the    center of the restrainer. A fully prone position, i.e. animal lying    on its stomach, was tested in marmosets and found to be acceptable    for fMRI in awake monkeys.-   Step 3. The head and body restrainers are fitted into supports that    can be screwed into the front and back plates. The body supports    have rubber gaskets at their contact with the plates to help isolate    any body movement.-   Step 4. Male rhesus monkeys (4-5 kg) are examined under imaging    conditions as described above. Animals are lightly anesthetized with    ketamine and fitted into the head and body restrainer. When fully    conscious as measured by eye reflexes and vocalization (ca. 45-60    after the injection of ketamine) saliva is collected. The animal    holder slides into a large opaque tube having the bore dimensions of    the magnet. After thirty minutes another sample of saliva is    collected. The two samples of saliva are assayed for cortisol to    evaluate adaptation to the stress of immobilization. This repeated    each day for several days and throughout the training period. If    salivary cortisol does not return to basal levels then adjustments    can be made in the restraining device to reduce the immobilization    stress.

Appropriate RF volume coils can be used for anatomical and functionalimaging of rhesus monkeys. The system scaleable to accommodatedifferences in head size of these monkeys. The designs can be utilizedfor uniform imaging of the whole animal head, or they can be used togenerate a uniform transmit field for high sensitivity reception fromlocal regions of interest a phased array surface coils. The systems canbe efficiently tuned to one, two or three frequencies as desired, and tothe highest frequencies for the desired speed.

Two criteria are sought in a preferred coil for high field animalimaging. First, the coil must be as efficient as possible. Transmisionefficiency minimizes RF losses to heat and noise in the monkey.Reception efficiency from a desired field-of-view (FOV), maximizes theSNR. In imaging, spatial and temporal resolutions are proportional toSNR.

This third example relates to the functional neuroanatomy of seizures.Using the apparatus and method described above, the moment-to momentchanges in brain activity are examined to gain a greater understandingof the neuronal networks for seizures. Functional magnetic resonanceimaging (fMRI), as described above, is used to map brain activity withhigh spatial and temporal resolution in conscious animals. Functionalmagnetic resonance imaging is sensitive to changes in the ratio ofoxygenated and deoxygenated hemoglobin present in the tissue. Thesechanges are termed blood oxygenation-level-dependent (BOLD) and anenhanced signal reflects an increase in neuronal activity. In thisexample it was shown robust lateralized increases and decreases in BOLDsignal throughout the brain following pentylenetetrazole administrationat a dose that routinely causes generalized seizure.

Epilepsies are disorders of neuronal excitability characterized by therepetition of seizures. Identifying the sites in the brain involved inthe initiation of seizure activity, its propagation and generalizationis an important step towards a better understanding of epilepticdisorders. Seizures can be induced by administration of chemicalconvulsants in normal animals; thus, administration ofpentylenetetrazole (PTZ) in rodents elicits various types of generalizedseizures including tonic-clonic seizures. This example provides enhancedtemporal resolution by using functional magnetic resonance imaging(fMRI) in awake rats to further investigate the neuronal networksinvolved in PTZ-induced seizure.

Functional MRI using the BOLD technique is sensitive to changes inproton-signal intensity in tissues surrounding blood vessels. The levelof paramagnetic deoxygenated hemoglobin in the blood vessels alters themagnetic-susceptibility of the protons flipped by a radio frequencypulse. Increases in deoxygenated hemoglobin debase proton spins, shortenT2 relaxation time, and decrease signal intensity. Increased neuronalactivity is accompanied by an increase in metabolism concomitant withchanges in cerebral blood flow and volume to the area of activation. Thelocal blood flow exceeds oxygen uptake lowering the level ofdeoxygenated hemoglobin and increasing T2 relaxation time and signalintensity. With ultra high field magnetic resonance imaging andmultislice gradient echo pulse sequencing it is possible to followchanges in BOLD signal over much of the brain with high temporal andspatial resolution.

Sprague-Dawley rats (350-400 g) were separated into control andexperimental groups. All animals were lightly anesthetized with sodiumpentobarbital (25 mg/kg; i.p.). A catheter of 20 gauge polyethylene wasinserted into the abdomen and held in place with surgical glue in orderto perform intra peritoneal injection. Animals were fitted into arestraining assembly 36, describe above, while control animals wereplaced in a small cage outside the magnet within the shielded room.After recovery from anesthesia, ca. 90 min, experimental animals wereimaged in a 4.7 T Bruker spectrometer using gradient-echo pulse sequence(TR: 146 ms; TE: 20 ms; flip angle: 300; data matrix: 128×128; filed ofview: 6.4 cm, pixel size: 0.5 mm; thickness: 1 mm). Images were obtainedat 18 sec intervals for over a 16 min period. For each experiment,baseline data were collected over the first 2 min interval, followed by3 min of data in response to the vehicle (0.9% NaCl) injection. Five minfrom the start of data collection animals were injected with PTZ at thedose of 50 mg/kg. Since it is not possible to observe PTZ convulsiveseizures in animals restrained for imaging, the control group was testedfor PTZ seizure susceptibility. These animals received the PTZ injectionat the same time as the experimental animals. In control animals, PTZseizures consisted of brief myoclonus jerks that evolve to forelimbclonus followed by generalized tonic-clonic activity with loss ofposture. The first generalized tonic-clonic seizure occurred about 2 minfollowing PTZ injection, and 2-4 seizural episodes were recorded duringthe next 5-10 min.

An example of activational maps for a single animal before and afterpentylenetetrazole (PTZ) injection are shown in FIG. 28. These data wereobtained by averaging six baseline data sets for each brain section andperforming a voxel-by-voxel subtraction of subsequent data sets. Red andyellow areas denote changes in BOLD signal above and below baseline byfive standard deviations. These activational maps were overlaid on highresolution anatomical maps collected at the same brain slice thus,providing accurate anatomical identification.

There was no change in BOLD signal following injection. Within 60 secafter PTZ injection there was significant change in signal mainly incorticolimbic areas that favored laterization to the left parietal andtemporal cortices. The first convulsive seizure occurred in the controlanimal at approximately 90 sec after PTZ injection. Activational maps atthis time showed a polarity and laterialization between increased anddecreased BOLD signal covering large areas of the brain, particularlythe cortex. In the data set immediately afterwards, the enhanced BOLDsignal in left cortical areas persists while the decrease in BOLD signalin other sites abates.

Changes before the occurrence of seizures, increased levels in BOLDsignal was found in an number of cortical sites including entorhinal,insular, perirhinal, parietal and temporal cortex as well as in thehippocampus formation. During PTZ seizures, BOLD activation exhibited alaterialized pattern. Thus, increased levels in BOLD signal was greaterin the cerebral hemisphere that exhibited an earlier neuronal activation(BOLD signal) following PTZ injection. The increased levels in BOLDsignal were mainly observed in cortical sites including perirhinal,insular, parietal, occipital and temporal cortex. No increased levels inBOLD signal were observed in the frontal cortex during PTZ seizures. Inthis example, BOLD signal was initially observed in the cortex in theleft cerebral hemisphere following PTZ injection. This unilateralpattern of BOLD signal was greater during PTZ seizures. In contrast, noincreased levels in BOLD signal was found in the right cerebralhemisphere following PTZ injection. Only,few structures were activatedduring PTZ seizures in the right cerebral hemisphere.

Changes in BOLD signal over time were also examined in a number of CNSsites. Among cortical sites, the dramatic BOLD activation was observedin the entorhinal cortex. Indeed, increased levels in BOLD signaloccurred immediately before PTZ seizures in the entorhinal cortex in theleft cerebral hemisphere, as compared to the one in the righthemisphere. BOLD signal increases in the entorhinal cortex weresustained over 12 min following PTZ seizures. Note that is this examplethe increased levels in BOLD signal was greater in the left cerebralhemisphere. The perirhinal, piriform, parietal and temporal cortex onlyexhibited a transient increased levels in BOLD signal concomitantly tothe occurrence of PTZ seizures. Like the entorhinal cortex, theolfactory bulb also exhibited a sustained increased in BOLD signal.Although BOLD signal was increased in the hippocampal formation in bothcerebral hemisphere, a unilateral pattern could be observed during PTZseizures. Thus, changes in BOLD signal in the left and right hippocampalformation was sustained during 12 and 6 min, respectively. A sustainedincreased levels in BOLD signal was also observed in both left and rightsubstantia nigra. Only modest and sporadic increased levels in BOLDsignal was observed in both left and right striatum, as well as in theseptum and superior colliculi. No changes in BOLD signal was found inthe thalamus and in the inferior colliculi.

Neuronal depression was also examined. In control, no neuronaldepression was observed. Immediately before PTZ seizures, neuronaldepression was only observed in few CNS sites including cortex (frontal,perirhinal, piriform, insular parietal, occipital and temporal),striatum and colliculi. However, a massive neuronal depression wasobserved during PTZ seizures, and was primarily localized in thecontralateral cerebral hemisphere that did not exhibit increased levelsin BOLD signal. Neuronal depression was observed in cortical sites(forebrain (striatum, septum, thalamus, hippocampus formation) andbrainstem (colliculi) sites as well as the cerebellum during seizures.During recovery from PTZ seizures, only few brain sites exhibitedneuronal depression.

The early increase in BOLD signal in cortical sites was dramaticallyincreased during convulsive seizure. Thus, the cortex is critical forthe pre-ictal and ictal phases of generalized seizure. Unfortunately, inthese studies the amygdala was obscured because of the susceptibilityproblems associated with T2* imaging around air-filled sinuses. Hence itwas not possible to evaluate the contribution of this important limbicarea in seizure initiation and propagation.

This example demonstrates that fMRI is useful to examine the propagationseizure activity in conscious animals. This technique revealed thespatiotemporal pattern of spreading BOLD, allowing identification of thesite of onset of seizure activity and its propagation. No dissociationbetween clonic and tonic network. This example further demonstrates thatit is possible to map neuronal activity-related signal associated withconvulsions in conscious animal using fMRI.

Referring to FIGS. 29A and 29B, an alternative front-end mounting plate294 is shown. The front-end mounting plate 294 has a plurality ofprojecting mounting rods 296 for engaging the surface of the tunnel bore212. The mounting rods 296 are slideably received in bores in thefront-end mounting plate 294. The mounting rods 296 have a biasmechanism, such as an elastic received on a protrusion 299 of each rodto retract the mounting rods. An adjustment handle 300 shown in FIG. 30is positioned in the hole has an adjustment mechanism, such a taperedshape that moves along the frame axis, to force the mounting rods 296outward.

The present invention demonstrates novel images of neuronal activationin conscious animals. Current methods utilizing anesthetized animals,which are known to exhibit dampened neuronal activity, may mask lowsignal levels. Furthermore, since the level of arousal (conscious vs.anesthetized) is inextricably linked to behavior, the future use of thisassembly will be a significant step in providing a better understandingof the neural circuitry that facilitates behaviors such as responses tovisual stimulation, temperature regulation, and motor stimulation, inaddition to a range of different environmental stressors and developmental and intraneurodevelopmental studies. Therefore, researchersinterested in the brain and/or behavior (utilizing laboratory animals)will be further assisted in their analysis of the efficacy ofmedications, with the utilization of this assembly.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A dual coil system for magnetic resonance imaging, the systemcomprising: a surface coil; a volume coil having a cylindricalnon-magnetic core module having an outer surface and a longitudinalaxis, a cylindrical bore extending through the core module along thelongitudinal axis and defining an inner surface; a plurality ofconductive strip lines, the strip lines extending parallel to thelongitudinal axis on the inner surface of the core module; a pair ofcircuit boards carried at the ends of the core module; and a pluralityof resonating elements, each of the resonating elements including one ofthe strip lines and at lease one tuneable capacitor, wherein the volumecoil includes features formed therein that permit the volume coil to beslidably moved along the longitudinal axis along guide membersassociated with a frame.
 2. The dual system of claim 1 furthercomprising a transceiver unit having a RF transmitter and a RF receiver,the transceiver unit connected to the surface coil and the volume coil.3. A dual coil system for magnetic resonance imaging, the systemcomprising: a surface coil; a volume coil having a cylindricalnon-magnetic core module having an outer surface and a longitudinalaxis, a cylindrical bore extending through the core module along thelongitudinal axis and defining an inner surface; a plurality ofconductive strip lines, the strip lines extending parallel to thelongitudinal axis on the inner surface of the core module; a pair ofcircuit boards carried at the ends of the core module; and a pluralityof resonating elements, each of the resonating elements including one ofthe strip lines and at lease one tuneable capacitor; and a transceiverunit having a RF transmitter and a RF receiver, the transceiver unitconnected to the surface coil and the volume coil, wherein the volumecoil further comprises a plurality of shielding strips extendingparallel to the longitudinal axis on the outer surface of the coremodule and wherein the adjacent shielding strips are connected by atleast one capacitor attaching adjacent shielding strips at alternativeends of the shielding strips.
 4. The dual coil system of claim 3 whereinthe core module of the volume coil is formed of a dielectric materialand the strip lines of the volume coil are electroplated on the coremodule.
 5. The dual coil system of claim 4 further comprising a matchingcircuit for adjusting the impedance of the resonating elements to thatof the RF source and a filter for separating the high frequency RFsignal from interfering with the DC tuning/detuning signal.
 6. The dualcoil system of claim 4 wherein both the surface coil and volume coilhave a detuning circuit for detuning the resonating element and a RFdecoupling circuit for reducing interference between a DC detuningsignal and a RF signal.
 7. The dual coil system of claim 4 wherein thesurface coil comprises a single loop or a dome shaped coil having acurvilinear surface.
 8. A surface coil comprising; a curvilinear supportsurface having a concave inner surface and a convex outer surface; acircuit board assembly; at least a pair of conductive strips carried onthe concave inner surface; at least one capacitor connecting theconductive strips; and a tuneable variable capacitor, wherein there areat least four conductive strips carried on the concave inner surface andfurther comprising a resonating element including one of the conductivestrips on the concave inner surface, and a shielding strip on the convexouter surface.
 9. The surface coil of claim 8 further comprising: adetuning circuit for detuning the resonating elements; a RF decouplingcircuit for reducing interference between a C detuning signal and an RFsignal; and a matching circuit for adjusting the impedance of theresonating elements to that of a RF source.
 10. A dual RF resonatorsystem that is adapted to be variably positioned over an anatomicalregion of interest of a biological entity comprising: a volume resonatorhaving a plurality of conductive strip lines and being configured formounting on guide members so as to enable variable positioning andrepositioning of the volume resonator along a longitudinal direction byslidably moving the volume resonator along the guide members; and asurface coil having a plurality of conductive strip lines and beingconfigured to be integrated into a member so as to enable positioning ofthe surface coil along a vertical direction.
 11. The resonator of claim10, wherein the volume coil has a cylindrical non-magnetic core modulehaving an outer surface and a longitudinal axis, a cylindrical boreextending through the core module along the longitudinal axis anddefining on inner surface; the plurality of conductive strip linesextending parallel to the longitudinal axis on the inner surface of thecore module; a pair of circuit boards carried at the ends of the coremodule; and a plurality of resonating elements, each of the resonatingelements including one of the strip lines and at lease one tuneablecapacitor.
 12. The RF resonator of claim 10, further comprising: atransceiver unit having a RF transmitter and a RF receiver, thetransceiver unit connected to the surface coil and the volume coil. 13.The RF resonator of claim 12, wherein the volume coil further comprisesa plurality of shielding strips extending parallel to the longitudinalaxis on the outer surface of the core module and wherein the adjacentshielding strips are connected by at least one capacitor attachingadjacent shielding strips at alternative ends of the shielding strips.14. The RF resonator of claim 10, wherein the surface coil comprises asingle loop or a dome shaped coil having a curvilinear surface.
 15. TheRF resonator of claim 13, further comprising: a matching circuit foradjusting the impedance of the resonating elements to that of the RFsource and a filter for separating the high frequency RF signal frominterfering with the DC tuning/detuning signal.
 16. A dual RF resonatorsystem that is associated with a frame and is adapted to be flexiblypositioned over an anatomical region of a subject comprising: a volumeresonator that includes a plurality of arranged conductive strip lines,the volume resonator having a plurality of longitudinal features formedtherein for mating with complementary guide members associated with theframe so as to enable the volume resonator to be slidably moved alongthe guide members in a longitudinal direction relative to the frame soas to permit variable positioning and repositioning of the volumeresonator relative to the guide members; and a surface coil thatincludes a plurality of arranged conductive strip lines and isconfigured to be integrated into a member so as to enable positioning ofthe surface coil along a vertical direction relative to the frame. 17.The RF resonator of claim 16, wherein the volume coil has a cylindricalnon-magnetic core module having an outer surface and a longitudinalaxis, a cylindrical bore extending through the core module along thelongitudinal axis and defining an inner surface; the plurality ofconductive strip lines extending parallel to the longitudinal axis onthe inner surface of the core module; a pair of circuit boards carriedat the ends of the core module; and a plurality of resonating elements,each of the resonating elements including one of the strip lines and atlease one tuneable capacitor.
 18. The RF resonator of claim 16, furthercomprising: a transceiver unit having a RF transmitter and a RFreceiver, the transceiver unit connected to the surface coil and thevolume coil.
 19. The RF resonator of claim 18, wherein in volume coilfurther comprises a plurality of shielding strips extending parallel tothe longitudinal axis on the outer surface of the core module andwherein the adjacent shielding strips are connected by at least onecapacitor attaching adjacent shielding strips at alternative ends of theshielding strips.